1. Field
This invention relates to configuration of multiservice access devices, more particularly to methods of configuring them to handle oversubscription and a multiservice access device capable of being oversubscribed.
2. Background
Multiservice access devices allow networks to handle all types of traffic such as voice, data and video. These devices are normally configured with a set number of permanent virtual circuits (PVCs) and switched virtual circuits (SVCs). Examples of this device include multiservice access switches and multiservice access concentrators.
PVCs are point-to-point configurations between devices connected by a network. They are configured before any traffic is sent, and once configured they remain in place. SVCs only exist as long as the two devices communicate, and are established at the time the transmission is required. As soon as transmission between the devices stops, the circuit is disbanded.
The disadvantage of PVCs lies in the configuration parameters of the connections. Since the circuits are established ahead of time, they typically are configured with a type of service. The type of service specifies the nature of the transmission rate for the PVC. The services include constant bit rate, variable bit rate-real time, variable bit rate-non-real time., and unspecified bit rate. The first three have guaranteed throughputs, and constant bit rate service has a constant throughput as well. PVCs connected with unspecified bit rates do not have guaranteed throughputs.
Multiservice access devices that utilize PVCs for handling traffic typically handle oversubscription on the device by converting oversubscribed PVCs to unspecified bit rate service. Therefore, a method and apparatus is needed that will allow oversubscription in a more efficient manner and increase the usefulness of the device.
One aspect of the invention is a method for configuring permanent virtual circuits in a multiservice access device. At least one of the permanent virtual circuits is configured as an oversubscription permanent virtual circuit (OS PVC). The configuration may involve configuring the OS PVC as a normal PVC with an added parameter of a timer. If the PVC is active, it can move into the OS state upon an absence of traffic for a time interval determined by a timer. Once it is in the OS state, traffic is monitored. If necessary the PVC is moved back to the active state to handle traffic. In one example, an OS designator is used to identify PVCs in the OS state, configured as unspecified bit rate PVCs. When the PVC becomes active, it is attempted to be configured as a normal PVC. If the bandwidth is not available, it returns to the unspecified bit rate configuration.
Another aspect of the invention involves modifying the traffic shaping process. This is done my having multiple entries competing for the same cell transmit opportunity in the calendar table. Also, the introduction of a service queue will handle the multiple entries in the traffic shaping table (calendar). The service queue is serviced in a first in first out manner.
Another aspect of the invention involves configuring some of the PVCs as OS PVCs by adding them to a service queue, as necessary. The PVCs in the service queue are defined as being oversubscription PVCs. The service queue is handled in a sequential fashion until empty.
Another aspect of the invention is a multiservice access device that can be configured for oversubscription.